Conventionally, a magnetic sensitive element 4, which is used with a magnetic encoder or the like, is secured to a holder 11 as shown in FIG. 12, and so arranged therein as to opposingly face a magnetic drum with a predetermined gap provided therebetween. As disclosed in, for example, Japanese Utility Model Laid-Open Publication No. Sho. 62-20,313, the holder 11 for such a magnetic sensitive element 4 comprises a positioning pin 11b and an adjustment slot 11a such that a machine screw 10 is inserted through the slot 11a with the pin 11b fitted into a positioning hole formed in a circuit board, thereby securing the holder 11 to the circuit board. The gap between the magnetic drum and the holder 11 can be adjusted by utilizing the slot 11a. Another type of holder is known in which, as shown in FIG. 13, an H-shaped separable holder 13, having the magnetic sensitive element 4 secured thereto, is combined with a fixed holder 12 having a pair of right and left guide walls 12a and a pair of right and left grooves 12b, the H-shaped separable holder 13 being fitted vertically in between the guide walls 12a and the grooves 12b. This holder is also arranged to enable the aforesaid gap to be adjusted by moving the fixed holder 12 per se via right and left slots 12c formed in the fixed holder 12. The holder disclosed in Japanese Patent Laid-Open Publication No. Sho. 61-165,621 is, as shown in FIG. 18, separated into a movable holder 14 in which is secured a magnetic sensitive element and a fixed holder 15 for holding the movable holder 14. The movable holder 14 is movably accommodated in the fixed holder 15, and to move the movable holder 14 forwardly and backwardly via a gap adjustment screw 16 and spring 17 will effect a positional adjustment of the movable holder 14 relative to the fixed one 15.
However, if the slot 11a or 12c is to be formed which allows the holder 11 or 12 to be secured to the circuit board or the like so that the holder 11 or 12 can be moved for fine adjustment, it is necessary to form the holder into a shape projecting in the rightward and leftward directions. This results in disadvantage that it is impossible to miniaturize the holder because of the increased holder size. The holder shown in FIG. 18 also has the problem that the holder size increases since screw-mounting holes 18 for securing the fixed holder 15 to the board need to be formed on right and left sides. As a result, such a holder occupies a wide area on the board. Another problem is that costs increase since the machine screw 10 is used for securing the holder to the board and thus such working step as a tapping is needed. The arrangement in which the movable holder 14 is moved for adjustment by means of the gap adjustment screw 16 has the disadvantage that an extremely complicated and large structure is needed for accommodating the adjustment screw 16 and the spring 17.
As shown in FIG. 14, the magneto-resistive element 4 has a resistance pattern which is generally formed by a plurality of resistors R.sub.1, R.sub.2, R.sub.3 and R.sub.4. It is desirable that this resistance pattern, which faces towards a magnetic drum 8, should be disposed parallel to a tangent T extending to touch one point closest to the center of the magnetic sensitive surface 4a of a magnetic recording medium 9 secured to the magnetic drum 8. With the magnetic sensitive element 4 inclined by an angle .theta. with respect to the magnetic recording medium 9, the resistor R.sub.1, closest to the magnetic recording medium 9, is exposed to the strongest magnetic field, while the resistor R.sub.4, the most remote from the magnetic recording medium 9, is exposed to the weakest magnetic filed. This can also be seen from FIG. 15 which shows the effective magnetic filed strength of the magnetic sensitive element 4 with respect to the gap between the magnetic recording medium and the magnetic sensitive element 4. However, turning to FIG. 12, the holder structure is such that adjustment of the gap is performed by means of the positioning pin 11b and slot 11a, according to which, the magnetic sensitive surface 4a is inclined by angle of .theta. relative to a plane T parallel to the tangent T, with movement of the holder 11 for the gap widening purpose, and consequently the resistance pattern is not set in parallel with the magnetic sensitive surface 4a. The holder structure as in FIG. 13, which has the slots 12c on the right and left sides, has a similar problem in that it is difficult to move the magnetic sensitive element 4 in parallel. In the case of the holder structure of FIG. 18 in which the movable holder 14 is moved for fine adjustment and secured in position by using the adjustment screw 16, since the movable holder 14 is not fixed to the fixed holder 15, the position or the inclination of the movable holder 14 may be shifted due to various factors such as vibration or a change in the position or the direction in which the elastic force of the spring 17 is to be imparted. This may possibly lead to a deterioration in output characteristics.
The resistors R.sub.1 to R.sub.4 are generally connected together as shown in FIG. 16, and, if difference occurs in magnetic field strength among those resistors, an A-phase output becomes larger than a B-phase output. In addition, difference also occurs in sensitivity among the resistors R.sub.1 to R.sub.4, affecting resulting output waveform to show a biased ratio of the positive part to negative part in that waveform and producing the fluctuation of an output signal due to jitters. The smaller is the magnetizing pitch of the magnetic recording medium, the more serious becomes such output problem. Hence, in this particular prior art, with increase of the angle .theta. between the magnetic sensitive surface 4a and the tangent T (or the parallel plane T.sub.1) associated with the magnetic recording medium 9, several electrical characteristics involved are more subject to enormous variations. Such is the case as shown in FIG. 17, wherein, as the angle .theta. is greater, a resulting waveform is shown to be distorted by the solid line d in reference to a dashed line c indicative of ".theta..apprxeq.0", which means deterioration of the output characteristics involved.